1. Field of the Invention
This invention relates to filters for use with aquariums and more particularly to "free standing" filters, which rest on a surface spaced from the aquarium as opposed to the filters of a type which are attached to the side of the aquarium. Still more particularly, the present invention is directed to an aquarium filter having improved filtering efficiency while maintaining convenient operation.
2. Description of the Prior Art
In order to simplify filter cleaning, aquarium filters of the "nesting" type have been developed in which an upper unit containing a filter cartridge is provided which mates with a lower unit having a motor contained therein. The upper unit contains a pump section having a rotatable impeller which is driven by the motor. The bottom of the upper unit is closed and there is therefore no direct contact between the motor and the impeller. The closed design enables the upper section to be removed for convenient cleaning and filter replacement. In order to drive the impeller, a first disc-shaped magnet is coupled to the motor shaft and a second disc-shaped magnet is coupled to the impeller. The impeller is thereby magnetically coupled to the motor and rotation of the motor shaft results in rotation of the impeller. Systems such as this are shown in U.S. Pat. Nos. 3,273,717 to Canterbury and 4,093,547 to Sherman, et al. Both patents disclose a nesting-type filter. The Canterbury patent is directed to a free standing aquarium, whereas the Sherman, et al. patent is directed to a filter which is attached to the side of an aquarium.
Although the nesting feature of such units provides a great deal of convenience in terms of servicing the aquarium, the inability to directly drive the impeller impairs the efficiency of such filters. As a result, this type of filter generally has not been suitable for heavy duty applications due to its relatively limited ability to pump water at high rates. This lack of drive power has also prevented the use of fine filtering media, such as diatomaceous earth, with such filters, since they are unable to develop the requisite pressures within the filter.